Engines produce mechanical output through combustion of a mixture of air and fuel inside cylinders of the engine. Flow of the mixture into the engine cylinders is typically regulated by intake valves that are opened and closed by a cam arrangement, which is operatively connected to a crankshaft of the engine. The rotation of the crankshaft results in a corresponding rotation of a camshaft that drives cyclical movement of one or more cam followers. The cyclical movement of the cam followers results in the actuation of the engine valves. During a typical combustion cycle, the cam arrangement opens each intake valve only during the time period in which the corresponding piston is traveling from top-dead-center (TDC) to bottom-dead-center (BDC). However, in some situations, the timing of the intake valves may be altered, such as during a late inlet closing (LIC) timing, in which the intake valves are left open longer and are not closed until after the piston has started traveling back toward TDC.
Gaseous-fueled engines utilizing a LIC timing instead of conventional timing may produce higher mechanical output and reduced emissions. However, LIC timing may not be ideal for engine startup if the valves close too late. Since the intake valve is open for a longer period of time during LIC timing operation, some of the air and fuel mixture in the cylinder is forced back out through the intake port, reducing the amount of charge (air/fuel mixture) in the cylinder at the time of possible combustion. While this process may have some benefits at higher speeds, the reduced charge may prevent sufficient combustion at startup of the engine.
An exemplary engine is disclosed in US Patent Application Publication 2007/0221149 by Ruiz ('149 publication). In the '149 publication, an internal combustion engine is disclosed that includes a hydraulically controlled cam phaser for adjusting the valve timing of the engine. A hydraulic pump powered by the engine supplies hydraulic fluid to the cam phaser to adjust the position of the cam phaser and thus, the engine timing. The '149 publication further discloses an auxiliary hydraulic pump powered by an electric motor for supplying hydraulic fluid to the cam phaser when the engine is shut down, such that the valve timing may be adjusted (i.e., advanced or retarded) for engine startup.
While the '149 publication discloses an engine with variable valve timing, it does not address startup of a gaseous-fueled engine that normally employs LIC timing. In contrast, the '149 publication discloses using the cam phaser to implement late inlet valve closing at startup. While these modes may improve engine startup efficiency in some applications at higher ambient temperatures, they may actually make starting more difficult for gaseous-fueled engines that normally employ an LIC timing when operating at high speeds. For a gaseous-fueled engine operating at low speeds, for example during engine startup, too much of the fuel/air mixture may be allowed to leave the combustion chamber, which is a problem that would not be addressed by altering the valve timing in the manner disclosed by the '149 publication. Further, since the cam phaser of the '149 publication requires an auxiliary hydraulic system, the engine may be overly complicated and consumer costs may increase.
The present disclosure is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.